1. Field of the Invention
The present invention relates in general to a compression release device for side-valve and overheadvalve internal combustion engines, and, in more particular, to such a device which comprises a structural arrangement including the use of materials different in linear expansion on heating for the engine parts in such a manner as to cause either or both of the intake and exhaust valves, upon the compression stroke of the engine, to remain slightly open at cold starting, while stay fully closed when the engine temperature is sufficiently high, as a result of the parts having undergone a different rate of thermal expansion.
2. Description of the Prior Art
When starting the engine at cold state under low temperature environment, it is necessary for either or both of the intake and exhaust valves to remain slightly open on compression so as to lessen the degree of pressure in a cylinder, easing crankcase rotation until the engine is brought to sufficient acceleration. Furthermore, provision must be made to cause the intake and exhaust valves to stay fully closed upon each compression when the engine is sufficiently warmed up for normal running.
To solve this problem, various devices have so far been developed in the prior art. For example, the use of an eccentric cam is disclosed to cause the rocker arm to move down or the push rod to lift upward in such a manner to provide control of the valve opening. In some other instance, valve opening is controlled by a mechanism by which the tappet is lifted relative to its cam.
Another more improved system proposed in the prior art provides automatic valve opening control by governing the operation of the cam in response to its rate of rotation. Typical examples of these conventional art are disclosed by Takeshi Yoshida, Discourse on the Internal Combustion Engine (Earth Ltd., Nov. 5, 1980) p. 384 and in published Japanese patent application No. 53-37981.
However, these conventional devices have various problems. First, they have been incorporated into the engine valve system as an additional mechanism having parts relatively complicated in structure. This also have increased the overall engine weight and decreased serviceability, without mention of their difficulties in treatment.